FWIW, I had this "side tone" issue on all three of my C lines (over the years).. I always just dissmissed it as a harmless anomaly.. Thanks for the advise! Maybe there is hope.
Ken Lotts aa7jc Sierra Vista, AZ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Robert Schenck Sent: Tuesday, November 11, 2003 7:28 AM To: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: RE: [drakelist] R4C/TX4C Sidetone Problem Hi Paul, You are probably hearing the T4X-C carrier oscillator getting into the R4-C. You can see if the signal is reduced or goes away if you unplug the carrier cable between the T4X-C and the R4-C. The key to this is that you loose the tone when the T/R relay goes to receive. IN CW mode, the mic preamp is used as a phase shift audio oscillator at about 700-800 Hz that is running all the time. This audio tone is passed, via the key action removing the forward bias on CR15, and this allows the audio tone to key the vox circuit, and also output over the VOX Anti-trip/ sidetone cable to get to the output transformer of the R4-C. The VOX circuit then powers the T/R relay. One of the functions of the T/R relay is to enable the carrier oscillator, Q2. IN SSB mode, the 5645 KHz output of the carrier oscillator is bufferd by Q2 and sent to the R4-C carrier input jack to lock the R4-C's carrier oscillator to the T4X-C. But, when in either CW, or AM, the carrier is pulled off frequency by about 750 Hz so that it can pass through the sideband filter. In both CW and AM, the mode switch disconnects the signal output to the carrier jack, and, a negative DC bias from the R4-C, by means of the VOX Anti-trip / sidetone cable, diables the carrier oscillator output buffer Q2. The symptoms you describe suggest that the T4X-C carrier oscillator is getting into the R4-C where it is heard as the fixed weak tone. It will not change pitch by tuning. The cut off bias is provided therough a high resistance in the R4-C. You should measure the voltage with a high impedance meter on the VOX Anti-trip / sidetone cable with it disconnected form the T4X-C. it should be around -55 volts or so. IF the voltage coming out of the R4-C is ok, then there may be excessive leakage in either C104 or C105...they couple AC in the VOX Anti-trip / sidetone circuitry in the T4X-C. IF they leak and reduce the negative DC bias, the carrier oscillator buffer may porivde enough signal to leak out of the T4X-C and into the R4-C. It is unlikely that it is sidetone itself leaking, since the tone goes away during receive. Of course, if there is not sufficient bias from the R4-C, the problem is in the R4-C. I beleive there is a .05 uF RF bypass cap or a coupling cap in the VOX Anti-trip / sidetone circuitry in the R4-C and it could also be a source of leakage. Well, at least this may give you a place to start looking. 73's Rob K2CU \ >[EMAIL PROTECTED] wrote: >While sending cw a steady, but weaker tone, is heard in the background. It >continues until the relay switches back to receive. Any suggestions as to what >part or parts have deteriorated? Thanks >Paul >K7CKZ > > __________________________________________________________________ McAfee VirusScan Online from the Netscape Network. Comprehensive protection for your entire computer. Get your free trial today! http://channels.netscape.com/ns/computing/mcafee/index.jsp?promo=393397 Get AOL Instant Messenger 5.1 free of charge. Download Now! http://aim.aol.com/aimnew/Aim/register.adp?promo=380455 ---------------------------------------------------------------------- Submissions: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] - subscribe drakelist in body Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Brought to you courtesy of TLCHost.net http://www.tlchost.net/ ---------------------------------------------------------------------- ---------------------------------------------------------------------- Submissions: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] - subscribe drakelist in body Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Brought to you courtesy of TLCHost.net http://www.tlchost.net/ ----------------------------------------------------------------------
